Investigating the effect of cryogenic pre-cooling on the friction stir processing of AZ31B

摘要

This manuscript aims to investigate the effect ofcryogenic in-process cooling via liquid nitrogen on theoutcomes of the friction stir processing (FSP) of twin roll cast(TRC) magnesium alloy AZ31B. Friction stir processing wasperformed on 3mm thick sheets of TRC AZ31B at a wide rangeof processing parameters. The tool rotational speed was variedbetween 600 RPM and 2000 RPM while the tool feed ratevaried between 75 mm/min and 900 mm/min. Thrust force andtorque values were experimentally measured using a 4-component dynamometer. Temperature measurements weremonitored during the different tests using Infrared sensors andthermocouples. The microstructure of processed samples wasobserved using optical microscopy. It was found that thrustforce and torque values of the pre-cooled samples were 5%higher than those of the room temperature samples due to thematerial hardening induced by the cooling effect. Finer andmore homogenous microstructure was observed for the precooledsamples when compared with samples processed at roomtemperature. The average grain size of pre-cooled samples waspredicted using a relation -previously introduced by theauthors- that relate grain size and the Zener-Hollomonparameter for TRC AZ31B. This equation was found tocorrectly predict grain diameter for in-line cooled FSP AZ31Bsamples at temperatures lower than room temperature.